Various forms of minimally-invasive thermal therapy are currently under development for treatment of localized prostate cancer. They include brachytherapy, hyperthermia, laser therapy, focused ultrasound, focused microwave, and cryosurgery. These local treatments could offer significant advantages over current standards of treatment such as radical prostatectomy, and external beam radiation therapy. However, safe and effective use of local thermal methods will require real-time monitoring of tissue temperatures and irreversible thermal damage during the procedure. Previously as part of a Phase I SBIR supported by the National Cancer Institute, we developed an interactive, image-guided laser-computer system capable of real-time, non-invasive monitoring of tissue temperatures and prediction of irreversible thermal damage using MR thermometry. Based on the calculated temperature, the system provides feedback control for producing laser photocoagulation lesions of a desired size. In this proposal we plan to adapt the system for use in monitoring and feedback control of laser therapy for the treatment of localized prostate cancer. We will perform testing and optimization of the system on in vitro and in vivo canine prostates. In Phase I the system will be developed around use of a low-cost diode laser source coupled to a diffusing tip optical fiber placed transurethrally. In the second phase, we plan to expand the system capabilities to be compatible with newer interstitial laser approaches using multiple sources and fibers as well as focused ultrasound and microwave therapies. PROPOSED COMMERCIAL APPLICATIONS: The interactive, image-guided, computer-controlled thermal therapy system developed during this research will allow minimally invasive thermal therapy in prostate and other deep tissues to be performed in a safe and effective manner. There are some 5000 clinical MRI scanners in the US currently and open MR scanners are increasing in popularity, thus the potential market for MRI-ready thermal therapy is significant. In addition to laser therapy for localized prostate cancer, the system will be useful in any application where non-invasive monitoring and control of tissue temperature is required including microwave, ultrasound, and radiofrequency.